Preparation of cyclopentadiene



Patented Mar. 23, 1948 UNITED STATE 'ATEN OFFICE PREPARATION OFCYCLOPENTADIENE New Jersey No Drawing.

This invention relates to cyclization. Specifically it relates to thedehydrogenation and cyclization of dehydrogenatable hydrocarbons, having5 carbon atoms per molecule, especially 1,3 pentadiene. Morespecifically the invention is concerned with a commercially feasibleprocess for the conversion of pentane or 1,3 pentadiene to 1,3cyclopentacliene.

As stated, the invention is applicable to the dehydrogenation andcyclization of pentane to 1,3 cyclopentadiene. This conversion isconsidered to take place by way of l-pentene and 1,3 pentadiene.Accordingly, the invention will be described with reference to theconversion of 1,3 pentadiene to 1,3 cyclopentadiene to which it isDre-eminently suited. These reactions can be represented as follows:

(i-pentene) =(3-H (1,3 pentadiene) According to the invention, 1,3pentadiene in pure form, or admixed with normal pentane and/or normalpentenes, or other gases, is contacted with silica gel at an elevatedtemperature for a time sufficient to effect a desired extent ofconversion to 1,3 cyclopentadiene.

The silica gel employed is an activated silica gel having goodabsorptive properties. The silica gel will have the properties andcharacteristics of activated silica gel commercially available.

The temperature employed for the dehydrogenation of the hydrocarbon, inthe instant case 1,3 pentadiene, will vary depending upon the otherconditions of operation and on the nature or Application November 24,1945, Serial No. 630,691

5 Claims. (Cl. 260-666) purity of the charging stock. However, theconversion of 1,3 pentadiene can be advantageously effected at atemperature within the range 300 C. to a temperature at whichsubstantial decomposition of the hydrocarbons will take place. Morespecifically a temperature within the range 400 C.-700 0., preferably450 C.650 C., can

be employed.

While the conversion per pass is substantially independent of pressureit has been found that lower pressures seem to form higher yields onrecycling. Accordingly, while higher and lower pressures are notexcluded from the scope of the invention, pressures in the range of 1000mm. Hg-lO mm. Hg, preferably 200 mm. Hg-lO mm. Hg, can be employed.

The time of contact of the 1,3 pentadiene with the silica gel is afactor to be considered. There is an optimum range of contact timecorresponding to charging rates of 0.25 gram/minute/IOO grams-10grams/minute/IOO grams of silica gel. However, higher and lower chargingrates are not excluded from the scope of the invention.

Example 350 grams of 1,3 pentadiene were charged at a rate of 10grams/minute at a pressure of about ,760 mm. Hg to 1000 grams of silicagel in a conversion tube at a temperature of 600 C. The efiluent fromthe conversion tube was cooled, condensed and fractionated resulting ina yield of 29 grams of 1,3 cyclopentadiene. On recycle of theunconverted 1,3 pentadiene the yield is 47 grams.

The contact mass can be regenerated indefinitely to substantially itsoriginal activity.

The particle or pellet size can be varied. About 4 to 8 mesh has beenfound quite satisfactory. Obviously the particle size should not be toosmall in the sense that a large pressure drop across the contact mass isto be avoided if substantially the same pressure in all parts of theapparatus is desired, unless fluid or fluidized operation is employed.

It will be apparent to those versed in the art that wide modificationand variations are possible within the scope of the invention as definedin the appended claims, the essence of the invention being in thatdehydrogenatable hydrocarbons having 5 carbon atoms per molecule can bedehydrogenated and cyclized by contacting the same at elevatedtemperature and suitable pressure with silica gel as set forth hereinand in the appended claims.

We claim:

3 1. A process for the dehydrogenation and cyclization of 1,3 pentadieneto 1,3 oyclopentadiene which comprises contacting 1,3 pentadiene withsilica gel at a temperature of at least about 300 C. but notsubstantially above a temperature at which substantial decomposition ofhydrocarbons present will take place for a time sufficient to effect adesired extent of conversion.

2. A process for the dehydrogenation and cyc1i-' zation of 1,3pentadiene to 1,3 cyclopentadiene which comprises contacting 1,3pentadiene with silica gel at a temperaturev within the range 400 C.700C. for a time suflicient to efiect' a f desired extent of conversion.

3. A process according to claim 2 wherein the pressure is in the range1000 mm. Hg-10 mm. Hg.

4. A process for the dehydrogenation and cycli- V zation of 1,3pentadiene to 1,3 cyclopentadiene which comprises contacting 1,3pentadiene with silica gel at a temperature within the range 0 450C.-650 C'. at a pressure within the range is within the range 0.25-10grams/minute/IOO' grams of silica gel.

ROBERT M. KENNEDY. STANFORD J. HETZEL.

REFERENCES CIT D The following references are of record in the file ofthis patent:

* UNITED STATES PATENTS Number Name 7 Date 2,178,602 Morrell et al Nov.7, 1939 2,389,406 Bloch et a1 Nov. 20, 1945 2, 106,632 Pines et a1 Aug.27, 1946 OTHER REFERENCES Eglofi et 21.2 J. A. C. S., 61, 3571 to 3580(1939).

